Marking pen



FIG. 1 is a perspective view showing my new design for a marking pen,

FIG. 2 is a front view thereof,

FIG. 3 is a rear view thereof,

FIG. 4 is a left side thereof,

FIG. 5 is a right side thereof,

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom view thereof. 

The ornamental design for a marking pen, as shown and described. 